Avoid abomasal bloat in calves

However, in calves less than a month old it is the abomasum that is generally associated with distension. This article discusses the potential causes, signs and treatment of abomasal bloat in dairy calves.

What is abomasal bloat?

The pre-weaned calf relies primarily on digestion of milk in the abomasum (the fourth stomach) and small intestines. In the very young calf the first three stomachs (reticulum, rumen and omasum) are not sufficiently developed and the calf is considered to be a 'simple stomached' (monogastric) animal at this early age. The abomasum has an acidic environment which helps in the formation of the milk clot before its passage to the small intestines for absorption of nutrients.

Acute bloat syndrome is characterised by sudden distension of the abomasum to give the calf a bloated abdomen appearance on one or both sides. It typically affects calves less than three weeks of age that have previously appeared healthy.

In mild cases, calves may show only slight abdominal distension with a fluid or gas splashing sound, have inconsistent mild diarrhoea and mild depression. In severe cases, calves are usually off their milk, are dehydrated, show signs of discomfort such as kicking their abdomen or lying flat-out and have a severely distended abdomen. They may or may not have diarrhoea. Death can occur within 6 to 48 hours if the bloat progresses and is not relieved. This condition tends to occur sporadically in dairy calves and some herds have multiple cases at once.

What causes abomasal bloat?

The cause of abomasal bloat has not been fully defined but is almost certainly related to milk-feeding nutrition. Several risk factors have been identified and these include feeding large volumes of milk in a single daily feeding, fortified milk-feeding programmes, bacterial infections, lack of water, irregular feeding times and inadequate colostrum intake.

It is thought that the excessive gas production is due to the fermentation of high-energy liquid feeds such as those used in accelerated growth programmes or electrolyte feeds with inadequate water. The fermentation process occurs as a result of bacterial over-growth and production of enzymes in the abomasum.

Anything that slows down the rate of abomasal emptying can result in an accumulation of excess gas. In North America, high-osmolality electrolyte products and milk replacers have been identified as the primary risk factor of abomasal bloat on some farms. Osmolality is a measure of the concentration of particles in a solution and a high-osmolality milk feed can occur in fortified milk feeding programmes and/or when incorrect mixing rates of milk powder are used. Consequently it is important to ensure the correct mixing rates are used for the specific brand of milk powder, whether used alone or in an accelerated growth programme.

Abomasal bloat can also be seen in conjunction with abomasal ulceration causing a mechanical obstruction of the abomasum and facilitating the accumulation of gas.

How is abomasal bloat treated?

Prompt veterinary attention is required in an attempt to relieve the abomasal distension by either trochar or passage of a stomach tube. Placing the calf in a 'dog-sitting' position with the front legs elevated, whilst passing a stomach tube, can aid in the relief of gas. Antibiotics are sometimes indicated especially where bacterial infections are suspected. The specific treatment is determined on a case-by-case basis and at the discretion of the veterinarian.

The syndrome is likely to be caused by multiple factors and although the definitive cause is unknown, dietary management is integral in the control of outbreaks. Prevention of abomasal bloat should be aimed at consistent milk-feeding nutrition and consultation with a veterinarian prior to feeding high volume or fortified milk feeding programs.

Fortified milk feeding programs are not simply a matter of 'adding a bit of milk powder to whole milk'; the exact mix rate will depend on the individual farm's feeding system, frequency of feeding, brand of milk replacer used and the nature of the whole milk used to mix the powder with.

• Gemma Chuck is a veterinarian with The Vet Group in Victoria, Australia.